To control access to data in an information processing apparatus to keep internal data secret, a “locking” function to stop part or all of functions in the information processing apparatus has been broadly employed. For example, for a personal computer, there has been known the screen saver which operates a locking function based on a timer.
In a personal information terminal such as a portable telephone (to be referred to as “portable terminal” hereinbelow), a precise locking function is required; for example, Patent Document 1 discloses an electronic apparatus which changes a user authentication method (an authentication processing program) on the basis of the accumulated off time from the previous power-off point of time to the current power-on point of time.
In addition, Patent Document 2 discloses a portable terminal to be employed in combination with an authentication terminal which conducts user authentication through a dialog via a short-distant radio communication function; when a fixed period of time lapses after the last operation, the portable terminal automatically makes a transition to a locked state; and to operate the portable terminal again, user authentication with the authentication terminal is required.
Although being other than a locking function for an information processing apparatus, Patent Document 3 discloses a data storage which assigns a rank to data to be saved according to an significance degree determined on the basis of a type, capacity, an attribute, a creation date, a last access date, a last update date, and the like of data, to thereby save significant data in a storage medium having higher safety.    Patent Document 1: Japanese Patent Laid-Open Pub. No. 2003-122443    Patent Document 2: Japanese Patent Laid-Open Pub. No. 2006-221452    Patent Document 3: Japanese Patent Laid-Open Pub. No. 2003-6005